1. Field of the Invention
The present invention relates to a vessel steering system in which steering is performed by pivoting a propulsion means, such as an outboard engine or a stern drive system, on a swivel shaft.
2. Description of the Related Art
To date, there has been proposed a technology in which, as a steering apparatus for a small vessel or the like equipped with an outboard engine at the stern, the propulsion direction of the vessel is controlled and the vessel is steered by pivoting the outboard engine counterclockwise or clockwise on a swivel shaft (for example, Japanese Patent No. 2734041). A conventional apparatus disclosed in Japanese Patent No. 2734041 is a so-called multi-engine steering apparatus in which two outboard engines provided at the stern are operated in conjunction with each other so that steering is performed; the outboard engines are coupled with a differential lever by the respective tie rods, and the differential lever is pivoted through the operation of the steering wheel by the intermediary of a steering cable, so that the two outboard engines are pivoted in the same direction on the respective swivel shafts in conjunction with each other. In the case of the conventional vessel steering system disclosed in Japanese Patent No. 2734041, as an actuator for pivoting an outboard engine in response to the operation of a steering wheel, there can be utilized a mechanism in which a hydraulic cylinder is adopted.
In addition, to date, in a vessel steering system, there has been proposed a technology in which, by utilizing an electric motor, an outboard engine is pivoted on a swivel shaft so that a vessel is steered (for example, refer to Japanese Patent No. 2959044). A conventional apparatus disclosed in Japanese Patent No. 2959044 is provided with an electric actuator for pivoting a single outboard engine on a swivel shaft, a steering wheel sensor for detecting the pivoting angle and the pivoting direction of a steering wheel, and a controller for controlling the electric actuator based on an output signal from the steering wheel sensor. In the case of the conventional vessel steering system disclosed in Japanese Patent No. 2959044, the steering wheel and the electric actuator for driving the outboard engine are connected with each other by the intermediary of a cable in an electric manner only.
Moreover, to date, in a vessel equipped with a plurality of propulsion units, there has been proposed a multi-engine steering apparatus in which the respective propulsion directions of the plurality of propulsion units are controlled in such a way as to be different in angle from one another so that the vessel can travel in a lateral direction or the like through the propulsion force produced by the combination of the propulsion-direction vectors of the propulsion units (for example, refer to Japanese Patent Application Laid-Open No. 2000-313398). A conventional apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-313398 is provided with an operational drive unit for making each propulsion unit perform steering operation, a shift drive unit for driving each propulsion unit to any one of shift positions, a single operation stick to be manipulated in an arbitrary direction with respect to a neutral position, and a control unit for controlling the respective motors of the drive units based on a signal corresponding to the operation position of the operation stick.
As described above, in the conventional multi-engine steering apparatus disclosed in Japanese Patent No. 2734041, the actuator for pivoting an outboard engine can be formed of a hydraulic cylinder. However, in the case where a hydraulic cylinder is utilized, there has been a problem that there is required a space, around the steering apparatus, where hydraulic tubes for the hydraulic cylinder are arranged and the structure becomes complex.
The conventional multi-engine steering apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-313398 is configured in such a way that the respective steering angles of the propulsion units can independently and freely be controlled; therefore, there has been a problem that the respective driving bodies forming the propulsion units may interfere with one another, whereby the actuator fails or damage to the driving body is caused.
The angle at which the respective driving bodies of the propulsion units start to interfere with one another depends on the size, the shape, the mounting position, and the like of an outboard engine or the like forming the propulsion unit. Therefore, in order to prevent the foregoing interference, it is required to adjust the mounting position of each propulsion unit and the control range of the steering angle, for each type of the propulsion unit such as an outboard engine or each time the propulsion unit is mounted on a vessel. Provided it is impossible to adjust the mounting position and the steering angle of each propulsion unit each time the propulsion unit is mounted on a vessel, a vessel whose stern has a broad overall width is required when the propulsion units are arranged in such a way that the respective driving bodies of the propulsion units never interfere with one another.
In the case of the conventional multi-engine steering apparatus disclosed in Japanese Patent No. 2734041, because of its structure, the respective driving bodies of the outboard engines do not interfere with one another; however, in the case of the conventional apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-313398, the propulsion units cannot be coupled with one another by use of a link mechanism such as the tie rod in the conventional apparatus disclosed in Japanese Patent No. 734041.